Power converter having temperature compensated output power

ABSTRACT

A power converter reducing a maximum available output power during extreme operating temperature conditions. The output power is adapted to be reduced during higher operating temperatures to maintain the power converter housing within acceptable operating temperatures. The power converter may then increase the available operating power as the converter housing temperature is reduced such that an acceptable output power is available during higher operating temperatures, rather than simply turning off the power converter during the excessive temperature condition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/213,117 filed Aug. 26, 2005, entitled “AC/DC Power Converter” whichis a continuation of U.S. patent application Ser. No. 10/790,654,entitled “Dual Input AC And DC Power Supply Having A Programmable DCOutput Utilizing A Secondary Buck Converter” now U.S. Pat. No.6,937,490, which is a Continuation of U.S. patent application Ser. No.10/072,074 filed Feb. 8, 2002, entitled “Dual Input AC And DC PowerSupply Having A Programmable DC Output Utilizing A Secondary BuckConverter” now U.S. Pat. No. 6,700,808 which is a CIP of U.S. patentapplication Ser. No. 10/005,961 filed Dec. 3, 2001, entitled “Dual InputAC/DC To Programmable DC Output Converter” which claims priority of U.S.Provisional Patent Application Ser. No. 60/335,785, filed Oct. 31, 2001,the teachings of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention generally relates to the field of powerconverters, and more particularly to a dual input AC and DC toprogrammable DC output power converter.

BACKGROUND OF THE INVENTION

As the use of mobile electronic products, such as PC notebooks, PDAs,cellular telephones and the like, continues to increase, the need forlow cost, compact power supplies to power and recharge these productsalso continues to increase. Most manufacturers of mobile productstypically include plug-in power adapters along with these mobileproducts to help facilitate the power supply needs of their customers.

Today's power adapters are typically AC-to-DC, or DC-to-DC powerconverters which are configured to either step-up or step-down the DCvoltage input delivered to the mobile device. With AC-to-DC adapters,for example, users can power most mobile devices by simply plugging theadapter into a simple AC wall outlet commonly found in most homes oroffices. Similarly, when only DC input power is available, such as in anautomobile or airplane, users can still power their mobile devices bysimply using a standard, off-the-shelf DC-to-DC adapter. Normally, bothadapters are designed and tailored to provide a regulated DC outputvoltage, which typically range from between 5VDC to 30VDC depending onthe kind of mobile device being powered.

Although these power adapters conveniently provide direct power andrecharging capabilities, users are often required to carry separateadapters to provide power to each individual mobile device. This oftenmeans that users have to carry multiple adapters: one for an AC inputpower source, and another for a DC input power source, moreover, userstypically carry multiple adapters to power multiple devices. Thus, bycarrying more than one device at a time, users of mobile product usersare forced to carry more than one bulk power supply adapter.

Accordingly, there exists a need for a power converter that resolves thesystem management problems associated with carrying all of the differentpower supply components necessary to power a wide variety of mobile orportable devices. Moreover, such a power converter would advantageouslyencompass serving the power supply needs of several different mobiledevices, as it would supply a filtered and regulated DC output voltagein response to either an AC and DC input voltage. Moreover, by having apower convert or having multiple output terminals, users have theability of providing power to several mobile devices of varying powerrequirements, simultaneously, regardless of whether the input voltage isAC or DC.

There is also a need for a power converter which is operable duringexcessive temperature conditions, and which reduces the likelihood thepower converter will completely turn off due to excessive operatingtemperature.

SUMMARY OF THE INVENTION

The present invention achieves technical advantages as a power converterreducing a maximum available output power during extreme operatingtemperature conditions. The output power is adapted to be reduced duringhigher operating temperatures to maintain the power converter housingwithin acceptable operating temperatures. The power converter may thenincrease the available operating power as the converter housingtemperature is reduced such that an acceptable output power is availableduring higher operating temperatures, rather than simply turning off thepower converter during the excessive temperature condition.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention and the specific embodiments will beunderstood by those of ordinary skill in the art by reference to thefollowing detailed description of preferred embodiments taken inconjunction with the drawings, in which:

FIG. 1A shows a block diagram of a dual input AC and DC power converterhaving dual DC voltage outputs in accordance with the present invention;

FIG. 1B shows an exploded view of the converter with the detachable buckcircuit;

FIG. 2 shows a schematic diagram of the power converter circuit asillustrated in FIG. 1 in accordance with the present invention;

FIG. 3 shows a detailed schematic diagram of a DC-to-DC buck convertercircuit in accordance with the present invention; and

FIG. 4 shows a detailed schematic diagram of the power converter circuitaccording to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The numerous innovative teachings of the present applications will bedescribed with particular reference to the presently preferred exemplaryembodiments. However, it should be understood that this class ofembodiments provides only a few examples of the many advantageous usesand innovative teachings herein. In general, statements made in thespecification of the present application do not necessarily delimit anyof the various claimed inventions. Moreover, some statements may applyto some inventive features, but not to others.

There is shown in FIG. 1A a block diagram of a dual input AC/DC powerconverter 10 having dual programmable DC voltage outputs in accordancewith the present invention. Preferably, the dual input AC/DC powerconverter 10 comprises a power converter circuit 20 having an AC-to-DCconverter 22, a DC-to-DC booster converter 24, a feedback circuit 26, afilter circuit 25 and a DC-to-DC buck converter 28. The power convertercircuit 20 is seen housed in housing 13 and advantageously provides afirst programmable DC output voltage at DC output terminal 16 and asecond programmable DC output voltage at terminal 18. Both of these DCoutput voltages may be generated as a function of both AC and DC inputvoltages.

In operation, the AC-to-DC converter 22 receives an AC signal via inputterminal 12 and provides a regulated DC output voltage at node N1.Similarly, the DC-to-DC booster converter 24 may receive a DC inputvoltage at its input via input terminal 14 and may also provide aregulated DC output voltage at node N1.

Input terminals 12 and 14 are integrated into a single common connector17 such that different power cords adapted to receive input power fromdifferent sources are received by the common connector 17. For instance,DC power from an airplane or car power source are wired to couple toinput 12 and AC source is wired to couple to input 14. In a selectedembodiment, the AC-to-DC converter 22 is adapted to generate a DC outputvoltage of between 15VDC and 24VDC in response to an AC input voltage atterminal 12 ranging between 90VAC and 265VAC. Likewise, the DC-to-DCbooster converter 24 is adapted to provide a DC output voltage which issubstantially similar to that of converter 22, but which is generated inresponse to a DC input voltage supplied at input terminal 14.Preferably, DC-to-DC booster converter 24 is adapted to receive avoltage in the range of between 11VDC and 16VDC. Advantageously,AC-to-DC conversion, via AC-to-DC converter 22, allows users of thepower converter 10 to power high-power mobile devices, such as a laptopcomputer wherever AC input power is available, such as in the home oroffice, for example. Conversely, the DC-to-DC booster converter 24 ofthe power converter 10 is capable of powering similar high-power devicesby stepping up most low amplitude DC input signals, such as those foundin automobile and/or airplane environments.

As shown, filter circuit 25 has its input tied to the respective outputsof the converter 22 and 24. In a preferred embodiment, the filtercircuit is adapted to provide a filtered DC output voltage at secondnode N2, which, thereafter, feeds output terminal 16, at an output powerof 75 watts, for example.

The single feedback circuit 26 is shown coupled to the output of filtercircuit 25 at node N2. In a preferred embodiment, the feedback 26circuit, through a single feedback loop, regulates the voltage level ofthe filtered DC output voltages generated by both converters 22 and 24.This single feedback loop regulate both converters 22 and 24 viaphotodiodes PH1 and PH3 by coupling the feedback signal to each feedbackpin 1 of the respective PWM circuit IC1 and IC2, as shown. Additionally,the feedback circuit 26 is adapted to receive a removable programmingmodule that allows mobile device users to provide a selectable DC outputvoltage at output 16 via node N2. The programming module comprises a key(tip) 15 comprising a resistor, wherein different associated values ofthe resistor establish different associated DC output voltages at output16. By allowing users to selectively change the voltage level of thefiltered DC output voltage, the power converter 10 may be adapted topower a variety of different mobile electronic devices, such as throughthe key (tip) 15, having different associated power requirements.Moreover, the power converter's 10 programming module may also beadapted to provide the additional function of output current limiting.

The DC-to-DC buck converter 28 has its input coupled at node N2,providing a second DC output voltage that is then fed to output terminal18, having an output power of 10 watts, for example. Preferably, buckconverter 28 discreetly steps down the filtered DC voltage and producesa second DC output voltage at a separate output terminal 18. In aselected embodiment, the buck converter 28 steps down the filtered DCoutput voltage to a range of about 3VDC and 15VDC. Advantageously, thissecond DC output voltage generated by converter 28 is independent of,and substantially lower than the DC output voltage at terminal 16. Thisallows users of the present invention to power not only a high-powerperipheral, such as a laptop computer, but also, a second, low-powerperipheral, such as a cell phone, PDA, and the like. Moreover, thepresent invention allows for these peripherals to be poweredsimultaneously by a single converter, regardless if the input voltage isAC or DC. The buck converter 28 is physically detachable from the mainhousing 13 as shown in FIG. 1B, allowing different buck circuitsproviding different output voltages to be selectively attached tohousing 13 and tap the DC output voltage from output terminal 18.

Referring now to FIG. 2 there is shown a schematic diagram of the powerconverter circuit 20 of the dual input AC/DC power converter 10 asdepicted in FIG. 1 in accordance with an exemplary embodiment of thepresent invention. As described herein in greater detail, the powerconverter circuit 20, in a preferred embodiment, comprises threeseparate converters: AC-to-DC power converter 22, DC/DC boost converter24, and DC-to-DC buck converter 28.

AC-to-DC Converter

The AC-to-DC power converter 22 includes a true off line switcher whichis configured in a fly-back topology. Full-wave rectification of an ACinput signal, received at input terminal 12, occurs using a full-wavebridge rectifier BD1 and a filter capacitor C1, which creates a DCvoltage bus from which the switcher operates. Inductor L1 offersadditional EMI filtering of the AC signal after the signal has beenrectified through the full-wave bridge. The AC-to-DC converter 22 alsoincludes a main controller IC1 configured as a current mode pulse-widthmodulator (PWM). Main controller IC1 is also configured to have asingle-ended output with totem pole driver transistors coupled thereto.The AC-to-DC power converter 22 has a main power switch Q1 which drivesthe main transformer T1. In a preferred embodiment, the transformer T1,Schottky diode D11, and filter capacitors C24 and C25 combine to providethe DC output voltage at node N1.

As noted earlier, filter circuit 25 allows for additional filtering ofthe DC output voltage derived from node N1. The filter circuit 25 itselfcomprises inductor L3, capacitor C26 and transformer NF1.Advantageously, the filter circuit 25 produces a filtered DC outputvoltage at output 16 having less than 100 mv peak-to-peak noise andripple.

The feedback circuit 26, through the single feedback loop, regulates thefiltered DC output voltages provided by the converters 22 and 24. Thefeedback circuit 26 is also adapted to be coupled to a removableprogramming module having a key 15, comprising resistor R53. As such,the present invention allows users to selectively program the DC outputvoltage later received at output terminal 16. The feedback circuit 26includes a photocoupler circuit comprising a pair of photocouplers PH1and PH3 connected in series (i.e., stacked), each being coupled to theoutputs of operational amplifiers IC4-A and IC4-B. Advantageously, thesephotocouplers are arranged along the feedback loop of the feedbackcircuit 26. Additionally, the feedback circuit 26 efficiently regulatesthe filtered DC output voltages generated by both converters 22 and 24through a single feedback loop. In stacking the photo-couplers, thepresent invention also allows the power converter 10 to maintain properinput/output isolation between respective terminals 12 and 14 and outputterminal 16.

Preferably, the output current limiting function of converter 22 isaccomplished via integrated circuit IC4A, resistors R33, R37, R38, andR39 and programming resistor R54.

Over voltage protection of AC-to-DC converter 22 is achieved usingphotocoupler PH2 and zener diode ZD2. In a preferred embodiment, zenerdiode ZD2 is set at 25V such that when in avalanche mode it causes thetransistor side of photocoupler PH2 to bias transistor Q1 into the onstate. When it is the on state, transistor Q3 pulls low pin 1 ofintegrated controller IC1 and pulls the operating duty cycle of theintegrated controller towards 0%. This takes the DC output voltage to 0volts. Also, when transistor Q1 is on, transistor Q2 is also forced onwhich then forces these two transistors become latched. If transistorsQ1 and Q2 are latched, input power must be recycled in order for thepower converter 10 to be turned on again.

DC-to-DC Converter

The DC-to-DC converter 24 is configured in a boost topology and utilizesthe same kind of integrated controller, IC2, as used in converter 22. Inthe DC-to-DC converter 24, transistor Q8 acts as the main power switchand diode D6 as the main rectifier. Preferably, inductor L2 is adaptedto function as a power boost inductor, which is comprised of a toroidcore-type inductor. It should be understood that the cathode leads ofdiodes D11 and D8 are connected, forming an ORed configuration,requiring only one output filter. Advantageously, this eliminates theboard space needed for a second set of filters capacitors.

Like the AC-to-DC converter 22, the DC-to-DC converter 24 is alsodesigned to operate at a frequency of around 80 KHZ. For the AC-to-DCconverter 22, the operating frequency is set by resistor R13 andcapacitor C7. Likewise, the operating frequency of the DC-to-DCconverter 24 are set by resistor R28 and capacitor C28.

The DC-to-DC converter 24 includes an over-voltage protection circuitcomprising zener diode ZD2, resistor R23, R24, R48, transistor Q415, andsilicon-controlled rectifier SC1. Zener diode ZD2 sets the over-voltageprotection point (OVP) which is preferably set at 25VDC. Generally,there is no current flowing through resistor R48. If, however, whenzener diode ZD2 begins to conduct current, the drop across R48 issignificant enough to bias transistor Q6 on, pulling its collectorterminal high, and thereby turning silicon controlled rectifier SC1 on.When silicon control rectifier SC1 is on, it pulls pin 1 of theintegrated controller IC2 low. Thus, if pin 1 of integrated controllerIC2 is low, the output drivers thereof are forced to operate at a dutycycle of 0%, thereby producing a DC output voltage of 0 volts at pin 6.Advantageously, the silicon controlled rectifier SC1 functions as apower latch circuit that requires that input power be recycled in orderto turn on the power converter 10 if a voltage above 25VDC is detectedat node N1.

The temperature of the housing 13 of the power converter 10 is monitoredusing a thermistor NTC3. If, for example, there is a correspondingincrease in the temperature of the housing 13, it will result in adecrease in the resistive value of thermistor NTC3, thereby causingtransistor Q9 to turn on and pull low pin 1 of integrated circuit IC2 ofconverter 24. Moreover, this causes the photo-coupler PH2 to be biasedenough to activate a latch circuit comprising transistors Q1 and Q2 thatwill shutdown the power converter 22. In addition, the power converter's10 thermal protection feature is adapted to operate regardless ofwhether an AC or DC input voltage is being received at their respectiveinput terminals.

FIG. 3 shows a detailed schematic diagram of the DC-to-DC buck converter28 in accordance with the present invention. The buck converter 28 hasan integrated circuit controller IC1, similar to converters 22 and 24,which is adapted to generate an on-time duty cycle to power transistorswitch Q1. The operating frequency of controller IC1 is set by capacitorC6, which is coupled between pin 4 of IC1 and ground, and resistor R1,which is coupled between pins 4 and 8. In a selected embodiment, thediode D1 functions comprise a Schottky diode and functions as “catch”diode. Inductor L1 is a output power inductor and couples the gate ofpower transistor Q1 to V_(out). Fuse F1 is shown coupled between V_(in)and the drain terminal of power transistor Q1, and advantageouslyprovides current protection to buck-converter 28.

Furthermore, the input V_(in) of the buck converter 28 is coupled to theoutput of filter circuit 25 at node N2, wherein V_(in) receives thefiltered DC output voltage therefrom. In a preferred embodiment, theinput of the buck converter 28 is coupled to output terminal 18 andprovides a second DC output voltage at V_(out). Advantageously, the buckconverter 28 discreetly steps down the filtered DC output voltage andprovides a second DC output voltage at output terminal 18 which isindependent of, and substantially lower than the DC output voltage atoutput terminal 16. A cable is not required to be connected to output 18for buck converter 28 to operate. Likewise, the DC output voltage of thebuck converter 28 enables users low-power peripherals, such as, a cellphones, a PDAs, and/or similar mobile devices. In a selected embodiment,the buck convert 28 may also be adapted to provide a DC output voltageat output terminal 18 ranging between 3VDC and 15VDC, selectivelydetermined as a function of the chosen value of resistor R1 used in theparticular buck converter 28, with a total power delivery of 10 watts,for example. As previously mentioned, the buck converter 28 may behoused in a separate, detachable program module that enables users toselectively program the DC output voltage at terminal 18 as a functionof different associated buck converter modules.

Referring now to FIG. 4, there is shown a detailed electrical schematicof a converter circuit 40 according to another preferred embodiment ofthe present invention. Circuit 40 is similar in many regards to thatshown in FIG. 2 and described earlier, wherein like numerals refer tolike elements, and contains some further features which will now bedescribed. In this embodiment, the temperature of the power converterhousing 13 housing this circuit 40 is also monitored using a thermistorNTC3 coupled thereto. However, in this embodiment, when there is anincrease in the temperature of the housing 13, the resistive value ofthermistor NTC3 will correspondingly decrease as a function of thehousing temperature, and the output power generated by circuit 40continues to be provided, but at a reduced power being a function of thehousing temperature. Thus, when the housing 13 heats up to apredetermined temperature, the power output of the circuit 40 willresponsively begin to decrease, such that the reduction in the outputpower reduces the housing temperature of the housing 13 to maintain thetemperature within a safe operating range, such as below a maximumtemperature (threshold) established by regulatory agencies. If thehousing temperature continues to increase, converter circuit 40responsively continues to decrease the output power available byconverter circuit 40. Should the operating temperature of housing 13eventually exceed the maximum temperature allowed, such as set forth byregulatory agencies, the converter circuit 40 will then responsivelyshut down. The power converter will remain shut down until the powerconverter is reset by the user, such as by removing the input power fromthe converter, and then reconnecting the input power to the converter,such as by removing and reattaching the input power cord to theconverter.

Still referring to FIG. 4, these features of circuit 40 are established,in part, by the combination of thermistor NTC3 and resistor R79 forminga resistive divide network with a node T defined therebetween. At anominal housing 13 operating temperature of, for instance, 25° Celsius,the resistive value of thermistor NTC3 may be 100 K Ohms. In contrast,if the housing 13 should have an operating temperature of about 86°Celsius, the value of the thermistor NTC3 may be about 9 K Ohms. Thethermistor resistance between 100 K Ohms and 9 K Ohms is generallylinearly related to the operating temperature of the thermistor, andthus the housing 13. For instance, there is a 61° Celsius voltage swing(delta) between this nominal temperature and the maximum allowedoperating temperature, and a 91 K Ohms resistance swing (delta) overthis temperature swing. Hence, should the operating temperature of thehousing 13 be about 50° Celsius, the resistance of thermistor NTC3 maybeabout 46.3 K Ohms.

Current limit regulation in the power converter circuit 40 is providedby operational amplifier IC4-A, which op amp generates a feedbackcontrol signal to the DC/DC PWM IC2 via the feedback loop, and also tothe AC/DC PWM IC1 the single feedback loop as previously described.Operational amplifier IC4-A provides current limit regulation, andoperational amplifier IC4-B provides voltage regulation.

The output current sense function is provided by resistor R18, (Ejaz,confirm this designation) which resistor R18 creates a voltage levelproportional to the associated output current level, and which voltagelevel is provided to the negative input of op amp IC4-A. When thevoltage level causes the voltage at the negative input of IC4-A toexceed the threshold voltage V_(th) at the positive input of op ampIC4-A, the output voltage level of op amp IC4-A changes, and theconverter circuit 40 responsively reduces the output power available atoutput 16.

The normal operating voltage level of threshold voltage V_(th) isestablished by the value of resistor R37, divided by the sum ofresistors R37, R39, and R71, times the reference voltage established byop amp IC5. Essentially, the voltage at node R is established by theresistive divide network formed by resistors R37, R39 and R71. Forinstance, if R37 has a value of 1.15 K Ohms, R39 has a value of 110 KOhms, and resistor R71 has a value of 33 K Ohms, and the referencevoltage established by op amp IC5 is 2.5 volts, then the referencevoltage provided at node R and to the positive input of op amp IC4-A isabout 19.4 mV.

By way of example, in an excessive operating temperature condition wheretemperature sensor NTC3 has reduced in value from 100 K Ohms at 25°Celsius to about 9 K Ohms at 86° Celsius (first threshold), thecombination of thermistor NTC3 and resistor R78 responsively willforward-bias diode IC7 such that the voltage at the nodes isresponsively reduced, with a proportional reduction of the voltage ofreference V_(th) at node R. Any further increase in the temperature ofthermistor NTC3 beyond this first threshold will consequently result ina further decrease of reference voltage V_(th) at node R such that theoutput power of circuit 40 available at output 16 will correspondinglycontinue to decrease. Advantageously, the available overall output powerof circuit 40 will thus reduce the temperature of housing 13 such thatit remains within its rated temperature limit.

In the event of a catastrophic condition, such as where the temperatureof housing 13 continues to rise after output power has been reduced inhalf, then the voltage at node T will responsively bias transistor Q15,thus biasing transistor Q9, which in turn provides a ground to node W,thereby biasing diode PH2 which biases transistor Q4, and the circuit 40shuts down thereby providing over voltage protection (OVP).

The embodiment shown in FIG. 4 provides the advantages of reducing theoutput power provided by the power converter when the temperature of thehousing 13, which is physically coupled to thermester NTC3, exceeds thefirst threshold, such as 86° Celsius. Any further increase in housingtemperature thereafter will correspondingly further reduce the outputpower of the converter 10 to help reduce the operating temperature ofthe circuit 40 and thus the housing 13. Thus, the available output poweris variable and a function of the housing temperature. If the nominaloutput power of circuit 40 is, for example, 70 watts, the availableoutput power of circuit 40 that can be drawn by a portable electronicdevice via output 16 will continue to decrease down to about 35 wattswhen the housing 13 is at the maximum allowed operating temperature,such as 100° Celsius (second threshold). If the housing temperatureexceeds this second threshold, then the circuit 40 completely shuts off,and manual resetting of the power converter circuit is required by theoperator before the converter circuit can be powered on again, aspreviously described.

Though the invention has been described with respect to specificpreferred embodiments, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentapplication. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

1. A power converter, comprising: a first circuit configured to an ACinput voltage to a first DC voltage; a second circuit configured to a DCinput voltage to a second DC voltage; a temperature sensor configured togenerate a signal as a function of a temperature; and a third circuitconfigured to receive the first and second DC voltages and, in responsethereto, provide a DC output voltage at an output, wherein the thirdcircuit is configured to provide a maximum available output power as afunction of the temperature sensor signal.
 2. The power converter asspecified in claim 1 wherein the third circuit is configured to reducethe maximum available output power as the temperature sensor senses thetemperature exceeding a first predetermined temperature.
 3. The powerconverter as specified in claim 1 further comprising a housing, thethird circuit being disposed in the housing.
 4. The power converter asspecified in claim 3 wherein the temperature sensor is coupled to thehousing.
 5. The power converter as specified in claim 4 wherein thethird circuit is configured to reduce the maximum available output poweras a function of the housing temperature.
 6. The power converter asspecified in claim 5 wherein the third circuit is configured to variablyreduce the maximum available output power as a function of thetemperature.
 7. The power converter as specified in claim 6 wherein thethird circuit is configured to reduce the maximum available output powerto zero when the temperature exceeds a second predetermined temperaturebeing greater than the first predetermined temperature.